Carboxy alkyl cellulose impression materials and impressions made therefrom



Patented Aug. 29,

CARBOXY ALKYL CELLULOSE IMPRESSION MATERIALS AND THEREFROM IMPRESSION MADE 7 Homer van Beuren Joy, Montclair, N. J assignor,

by direct and mesne assignments, of one-half to l'viontclair Research Corporation, a corporation of New Jersey, and one-half to Ellis- Foster Company, a corporation of New Jersey No Drawing. Application March 30, 1948,

Serial No. 18,065

24 Claims This invention relates to impression materials, and more particularly to dentalimpression materials, to substances and compositions in producing such impressions, to impressions made with these substances and compositions, and to methods of making such substances, compositions. and articles, and methods of utilizing the substances and compositions.

Various substances and compositions have been suggested in the prior art for the production of impression compositions and materials. The more exacting the art is in which such impression. material is employed, the fewer are the satisfactory materials thatnhave been employed for such purposes. For example, considering the exacting requirements of the dental impression art, there are few compositions which have proved satisfactory in practice and for the most part .they have been based on alginate containing compositions although pectates have also been proposed. The compositions have not always been satisfactory, many of them exhibit limited shelf-life, and arevsubject to other. de-

be of such physical character that it can be inserted into cavities and fissures and readily removed therefrom without mutilation or destruction when set; it should set in a suitable time, not too short to prevent proper manipulation in application, nor so long as to cause discomfort to a dental patient; it should form a sharp accurate impression of the structure to which it is applied; it should set to a tough rubbery or flexible state so that it may be stripped from the structure to which it has been applied even when undercuts are present; and the dry powder composition should be stable over a substantial period of time before mixture with water for use. Few compositions have been found to be, usable in the art. In some of them compressional strength is obtained at a sacrifice of flexibility. In some, the gel structure obtained is not satisfactory because it is rather loose and open in character. In some cases ions formed act as retarders for plaster which comes in contact with the impression, Because of these and other considerations, prediction isof little value and actual test is required to determine the actual value of any composition for the exacting requirements in this field. Whether or not the set obtained is weaker strong, and other factors mentioned above, must be investigated.

2 Among the objects of the present invention is the production of impression materials from substances giving satisfactory gel structures enabling impression materials to be produced without the defects exhibited by prior art materials.

Other objects include the production of impressionmaterials which possess high compressional strength and extreme flexibility when set.

Still further objects include molded impressions from such impression materials.

Many other objects and advantages in the invention will appear from the more detailed .description set forth below, it being understood that such more detailed description is given by way of illustration and explanation only, and not by way of limitation, since various changes therein may be made by those skilled in the art without departing from the scope and spirit of the pres-v ent invention.

In accordance with the present invention, impression materials are produced particularly suitable for dental impression use, from carboxy alkyl cellulose employed in a composition containing a salt of a metal forming a gel with the carboxy alkyl cellulose, the combination yielding a satisfactory gel structure when set from a paste with water. The carboxy alkyl celluloses differ radically from alginates and related ma-. terials heretofore used in the art in that the alkaline earth metal salts of the carboxy alkyl celluloses, namely, the calcium, strontium andbarium salts are soluble in water as well as the alkali salts thereof, thus distinguishing the carboxy alkyl celluloses from alginic acid and similar materials heretofore used in the art in requiring their utilization under essentially distinct condi- 'tions.

The carboxy alkyl celluloses include carboxy methyl cellulose, carboxy ethyl cellulose, and other carboxy alkyl celluloses but for present purposes it ispreferred to use a carboxy alkyl cellulose in which the alkyl group does not contain more than 4 carbon atoms, that is, not above the carboxy butyl cellulose and more desirablythe carboxy methyl cellulose is employed although the carboxy ethyl cellulose may also be satisfactorily utilized. For illustrating the invention, since it is particularly eminently suit- I able for use in this direction, the invention will be illustrated by the use of the carboxy methyl cellulose.

The carboxy alkyl celluloses individually or in impression work, long chain amine salts would not normally be employed because they give a soapy product in water. Consequently for dental impression work, the salts of sodium, potassium,

the soluble carboxy alkyl cellulosewhich jggmn ployed. Here too the carboxy methyl celluose may be used as exemplary. Carboxy methyl cellulose is available with a viscosity as high as 2000 C. P. S. at 1% and carboxy methyl cellulose of that viscosity gives the strongest impressions. It is'most desirably: employed although lower viscosity carboxy alkyl celluloses may be emplayed, as for example, that having'a viscosity at 1000 but below 1000 the strength drops off rapidly and at least for dental impression'work a lower limit of from 500 to 700 C. P. S. may be mentioned although the highest viscosity mate: rials-as set forth above give the most desirable impressionsfrom the strength standpoint.

With the carboxy alkyl cellulose, a setting agent is employed. Since the alkaline earth salts of'the carbosy alkyl celluloses are soluble in water, they are "not avaiable as setting agents. The setting agents employed should be a salt or. mixtures of saltso-ifa metal or metals iorming a gel with the carboxy alkyl cellulose when set from a paste with water. The metals, salts of which can be used'f'o'r forming strong gels are'more particularly those in classes Ib, Illa, IVb, VIa, and group VIII o f' the periodic system as exemplified tor exampleby copper, lead, aluminum, iron and chromium, which are capable :of forming strong gelswith" the cellulose solution. The salts employed-o-f such metals for setting purposes include for example, the halides, sulfates, silicates, acetates, etc. Thus chromic sulfate, lead halides, lead mono-silicates and other slightly soluble lead salts, 'alu-rn i-num'salts such as its salts with orgame acids particularly the acetates and more specificallythe'bas'ic aluminum acetates, etc., may be used. 'Salts which give the productiongof gels oi'satis'factory strength and compositions which are light orwl'i i-te color are preferred since they may lee-pigmented readily to any color to meet commercial acceptance. Aluminum acetate may be employed to give excellent compositions for these purposes with for example, carboxy methyl-cellulose; In some instances the aluminum triacetate by itselfmay be too rapid in setting and may be retarded by basic retarding agents such as the alkali metal carbonates and phosphates, as for example, sodium carbonate or sodium phosphate. The'best results, however, have been obtained by the use of basic aluminum acetates.

The speed of setting of the composition depends mainly 'on the degree of basicity of the aluminum acetate. This'varies considerably in commercially available basic aluminum "acetates. The acetic acid content of the basic aluminum acetate, therefore, affects the speed of setting of the ultimate composition produced. If the basic aluminum acetate employed'is relatively slow in its action, more of it may be employed with for example, sodium carboxy methyl cellulose in order to increase the setting time or the compositionl For example, considering proportions of basic aluminum acetate to sodium carboxy methyl cellulose where a 1:1 ratio gives too slow a setting 4 time, the amount of basic aluminum acetate may be increased for example, to a ratio of 5:1 or acidic accelerators such as the alkali metal bisulfates for example, potassium bisuliate maybe incorporated in order to speed up the setting time. Where the basic'a'luminum acetate is too rapid in its action, retarders may be incorporated,

: namely, basic retarding agents such as the alkali metal carbonates and phosphates for example, sodium carbonate or sodium phosphate. Basic acetates produced in the laboratory may becontrolled from the standpoint of their basicit'y to give the desired set. Commercially available basic aluminum acetates may be heat treated to reduce their acetic acid content where the commercially available material is too rapid in its action, reduction in the "acetic acid Lcoritent materially afi'ectingthe rapidity of action. For example, in one commercial basic acetate which had an aluminum oxide content of 33.4% and which was somewhat too fast in setting time with? out the use of a retarder, such basic aluminum acetate heated for 42 hours at 140- C. lost an appreciable amount ofacetic acid and gave ex? cellent results when used even in equal parts by weight with the sodium carboxy methyl cellulose for example.

To-exemplify the basicity of basic aluminum acetate, reference may be made to the commercial material which usually shows an analysisthat corresponds roughly to the formula AKQH 5. 9 2

. aluminum acetate and for that purpose'small amounts only are necessary. If 'desired, sub stances such as soluble sulphates, particularly potassium sulphate, which accelerate the setting of plaster, may be included in the impression composition, in small amounts as for example, from 0.5 to 5% by weight.

' it is possible to adjust the setting time of these compositions, as for example, by the char r ac terl oi the basic aluminum acetate or other i setting agent which is employed or by the pres:

ence of accelerators or; 'retarders, etc. The illustratiye setting times referred to herein are par ticularly stated from the standpoint of the utili zation of these compositions for the production 7 of dental impressions 'wner-eit is desirable that the composition should showcharacteristics which enable'them to b'eused so that there is avail-ableone minuteior mixing and a setting time or about 3 minutes.

As exemplifying other setting agents that may be employed the iollo w ingis giver-1'. Ghromic sulphate be used as the' setting agent. It exists in *a variety of forms which are not all equally efiective for these rmrposes. Ofthese varieties, the most important for use in compositions made under this in'ventionparticular-ly for dental impression materials, ma be characterized as the green chromic sulphates "which are hydrated salts. In their most desirable form, they contain at least one sulphate whichdoes not precipitate with barium chloride, and there may be 1, 2 or 3 such unreact-ive sulphate groups present. Those having from 5 to i3 molsofwater of hydration are particularly valuable and a specific salt oi that character is the chromic sulphate having an SO4/ 3T2O3 ratio ofabout 2.971 and having 7 .4 m o'ls of water hydratien. In general any delique soent chromic sulphate is-no't desirable but the non-deliquescent salts are used. Anyoi-the hydrated chromic. sulphates may be used, .including the'violet coloredisalt with 18 mols of water of hydration, if first heat treated,.as for example, at temperatures of from 99 to 150 C., or preferably from 90.to 110 C. convert them into lower hydrates particularly of green color. The rose colored anhydrous salt is desirably converted into a hydratedmaterial for use in the present invention.

While the chromic sulphate'employed may be produced in any desired way, as for example, heat treatment of higher hydrates within temperaturerangesas indicated above for periods of say about 5 hours or by direct preparation in. appropriate ways, the following example illustrates one manner of preparation of a satisfactory material-for use herein without any intention limitation to that example.

.Sulphur dioxide gas is passed into an aqueous Percent C12O3 26.17 Basicity 21.77 Acidity (as H2804) 39.69 Total S04 47.60 F6203 and A1203 .34 B20 (105 C. overnight) i 11.56

Clz None Chromic sulphate as pointed out above, is particularly useful in making impression materials specifically for dental impression work. Other chromic salts may be employed but toxic materials such as chromic fluoride are desirably not used in compositions for dental purposes.

Lead salts, particularly those having solubilities in the range of about 0.1 to 1% may be used.

Any slightly soluble lead salts may be'employed. Such said lead salts when used, should be capable of setting the carboxy alkyl cellulose or should be capable of being utilized with materials which .will give the desired setting in the composition.

Lead monosilicate (85% PhD, SiOz) alone will usually not set carboxy methyl cellulose but acid may be incorporated, as for example, in the form of acid salts to get the desired results so long as an insoluble lead salt is not formed. Thus potassium acid tartrate or potassum acid phthalate desirably in. small amounts may be used to obtain setting of the carboxy methyl cellulose for example, with lead monosilicate. Aluminum silicofluoride and zinc nitrate may also be employed with the lead monosilicate to produce setting. Lead'chloride PbClz is particularly useful in making materials for dental impression work and the soluble sulphates such as potassium sulphate are good retarders for use in such compositions containing lead salts. I

- As fillers; any substantially water-insoluble powder may be employed so long as it "does not exhibit excessive basicity. Because of the amphoteric character of aluminum hydroxide, fillers of high basicity are desirably avoided. Non-basic fillers such as silica, bari m sulfate, silicates and the like, may be employed. Calcium carbonate may e utilizecb ie s of i s 19W sol i yout er fillers that may beemployed include the various calciumgcarbonatesin their heavyorlight forms, clays, diatomaceous" earth, f chalk, bentonite, mica, asbestos, volcanic ash, hard waxes andfthelike... f 1 Magnesium carbonates are generally too basic to be used as fillers, but this depends in part on the setting agent employed in the impression material. For example, with some. grades of chromic'sulphate as illustrated below, magnesium carbonate may be used. Suchfiller usually makes up the bulk of the composition and has some influence on the final physical properties of the gel, influences the setting time somewhat, the working properties of the paste, and the fineness of the impression. Some fillers may exert a particular property of value in some cases, as for example, the use of volcanic ash to give smoothness and to improve hardness. Where the higher proportions of basic aluminum acetate are employed, the amountof filler used may be considerably reduced and'as much as one-half of such filler replaced .by the utilization of the higher proportions of the basic aluminum acetates forfexample. Very heavy fillers such as lead silicate may be used in quantities considerably more than the lighter'fillers.

The over-all proportions of thecomponents utilized should be capable of giving the desired gel structure when the composition is set from a paste with water. For example, with 1 part by weight of 2000 viscosity carboxy methyl cellulose there may be employed from 0.7 to 5 partslby weight of setting agent such as basic aluminum acetate dependent in part on the acetate content as explained above, and from 7' to 12 parts by weight of a fairly light filler such as diatomaceous' earth, whereas when a very heavy filler suchas lead silicate is used, the weight of filler may be up to 30 parts by weightand higher. As noted above, where a high proportion of setting agent such as aluminum acetate is used such as 5 parts by weight to 1 part by weight of the carboxy methyl cellulose, this may replace as-much as one-half of the filler, particularly the lighter fillers. Where lower viscosity carboxy alkyl celluloses are employed, as for example, in the 500 to 700 viscosity grades, the heavier fillers like lead silicate are preferably used and increased in amount, and desirably a greater'amoimt of the carboxy alkyl cellulose is employed. The materials referred to above are mixed with water for use and this may vary, enough water being employed to form a putty satisfactory for taking dentalor other impressions. In general with compositions of the character set forth above, the amount of water will usually be from 11 to 1'7 parts by weight with about 12 parts by-weight preferred, to 5 parts of'powden.

The following examples illustrate the invention, parts being by Weight unless otherwise indicated. a 1

v Example 1 Parts Diatomaceous silica 1 5 Basic aluminumacetate 5 Sodium carboxymethyl cellulose (2000 visc), 1 

1. AN IMPRESSION MATERIAL CONTAINING A WATERSOLUBLE SALT OF A CARBOXY ALKYL CELLULOSE IN A MIXTURE WITH A SETTING AGENT OF A SALT OF A METAL FORMING A GEL WITH THE CARBOXY ALKYL CELLULOSE, IN PROPORTIONS TO GIVE A GEL STRUCTURE WHEN SET FROM A PASTE WITH WATER. 